This invention relates to vacuum-tight seals made substantially of metal and more particularly to hermetically sealed envelopes and to hermetic seals.
Hermetic seals have a plurality of applications, such as housings for solid state devices, e.g., transistors, diodes and similar electronic components. The operating characteristics of electrical, mechanical or electronic devices located in an environment subject to temperature and pressure variations are affected by such variations. By housing such devices in hermetic seals, these characteristics are rendered relatively independent from temperature variations, pressure, vibrations, shocks, and air and moisture attacks. The teachings of the present invention are particularly suitable for the housing of electromechanical filters and resonators which must be mounted in hermetically sealed envelopes in order to improve their frequency stability and isolate them from outside tensions and forces.
A known hermetic seal between a tubular section and a base is described in U.S. Pat. No. 3,198,874 to W. F. Dahl, wherein a seal is formed by mechanically interlocking the tubular section and the base. In this known arrangement, the end of the tubular section which is to be interlocked with the base is provided with a series of flanges designated as stress ring, compression ring, and control ring. The base is provided with an annular groove adapted to receive the stress and compression rings of the tubular section. A hydraulic or mechanical press applies pressure to the tubular section in a direction parallel to its axis for permanently deforming the stress and compression rings of the tubular section within the annular groove. Although this known method makes no use of sealing adhesives or heat to achieve a hermetic seal, the series of flanges formed at one end of the tubular section must be carefully machined in accordance with a complex configuration of rings and recesses. Furthermore, a relatively high pressure is required to deform the rings and allow material from the base to flow into a labyrinth formed by the rings and recesses.
Another known vacuum-tight envelope consists of two metallic parts connected together by means of their respective flanges. In such a known arrangement as described in U.S. Pat. No. 3,182,117 to W. A. Roovers, one of the flanges is provided at its periphery with a sharp ridge with two flanks directed toward the other flange and pressed into the material thereof. The first flange is embraced by an edge of the other flange. Such an arrangement requires forces of the order of 750 kilograms in order to achieve a cold-welded envelope.